The present invention relates generally to aircraft detection systems, and more specifically to a system for detecting and tracking stealth aircraft using microcomputer-controlled adaptive arrays of seismic and acoustic sensors.
Conventional radio frequency (R.F.) radar systems possess certain natural limitations in the detection of low-flying aircraft. Terrain echo returns have increasingly greater tendencies to obscure tracking of aircraft as they approach the ground. Certain aircraft will intentionally take advantage of this limitation and fly low to avoid the radar of law enforcement agencies, border patrol officials, and military facility protection systems. With the advent of advanced weapons and aircraft technology, such as cruise missiles, stealth technology and ground-hugging guidance systems, radar has become a less reliable means for the detection of hostile aircraft penetration. The small radar cross sections of stealth aircraft and cruise missiles make them difficult targets under ideal conditions. With the addition of ground-hugging guidance systems, radar detection probabilities are further reduced as the target is concealed by ground clutter and topographic effects. Further, active sensors, such as radar, can be targeted and neutralized on the basis of their own signal.
Aircraft which are equipped with stealth anti-detection devices present an additional challenge, since they possess radar jamming systems which render them invisible to R.F. radar systems.
The task of providing a means of detecting stealth aircraft is alleviated, to some extent, by the systems of the following U.S. Patents, the disclosures of which are incorporated by reference:
U.S. Pat. No. 4,630,246 issued to R. J. Fogler;
U.S. Pat. No. 4,208,735 issued to Suzuki et al,
U.S. Pat. No. 3,824,532 issued to Vandierendonck;
U.S. Pat. No. 3,774,190 issued to Kyle, Jr.;
U.S. Pat. No. 3,852,706 issued to Barney et al; and
U.S. Pat. No. 4,083,031 issued to Pharo, Jr.
Stealth aircraft may be invisible to radar, but they are still subject to detection from their seismic and acoustic signatures. The Fogler reference is a detection system which uses a geophone and a microphone to detect low-flying aircraft.
The Suzuki et al patent discloses a moving sound source identifying system which uses a pair of spaced apart microphones and output circuitry which calculates the correlation function between signals produced by the two microphones. The system is said to differentiate between moving and stationary sources as well as flying and ground sources.
The Vandierendonck patent discloses a seismic signal intrusion detection classification system which detects a sound source, processes the sound and examines the characteristic pattern of the sound to provide classification thereof.
The Kyle, Jr. patent discloses an intrusion detection system which detects the sound source and processes the output signal through a signal processor. The source is identified from the vibrational signature of the process signal.
The Barney et al and Pharo, Jr. patents object locating systems which use a pair of hydrophones which detect acoustical signals, one of the signals being compared with the other after being delayed in time.
The references cited above have an advantage in that they do not rely on transmitted RF radar signals. Collectively, these references represent a recognition of the need to develop seismic and acoustic detection systems which are not dependent upon transmitted RF signals which can be jammed. The present invention is intended to help satisfy that need.